Air-compressor.



RD. HOLDSWORTH.

APPLICATION FILED` MAY 8 LN2.

Pmentd Nom 2?', M71

3 SHEETS-SHEET 3.

Dm l

l Wm? Mxm f sary to interrupt `the flow f or to thev .cylinder of r sata *Li un n. nounswo'rn, or .cn :.f Y assrennrnnrs, 'ro SULLIVAN To all .fwlwm t may concern.' Y

Be it known thatl, FRED D. Honnswon'rn, a' citizen of the United States, and a resident of Claremont, county of Sullivan, and State of N ew Hampshire, have invented an Imrovement in Air-Compressors, of which the ollowng description, in connection with the accompanying drawings, is a specilicati'on, like characters on the drawings representing like parts. i

This invention relates to elastic Huid compressors, and is applicable to the'low-pressure cylinder of a multi-stage compressor,

a single-stage com--` pressor, or te any cylinder beyond the intake cylinder of a multi-stage compressor.

In the operation of, air compressors which are driven by an external source of power which runs ata constant speed, such aselectric motors, gas or gasolene engines, in order to maintain aconstaiit pressure, it is necesof air through the machine 'when the pressure in the receiver 1s. piped to the main air x this unloading 35 d@ quantity of air Hows through the machine,

I te

` valve,A commonly `forms a more all of its internal thev construction of .to the main receiver,

sion is directly depen reaches the desired point, and restablish the flow as soon as the pressure in the receiver has fallen a few .ounds This is usually accomplished by placing a balanced called an unloading valve, main inlet supply to the compressor,

on the and attaching to this valve asuitable piston which moves thevalve to its open or closed Vposition by means of a small regulator which receiver. When valve'is closed bythe rise in the receiver pressure, the compressor rapidly or less complete vacuum in air passages. Ow' to this form of unloa ing valve, it is impossible to make it absolutely air-tight when it is closed, so thata smallA which air has to be compressed and applied `lnstead of compressing this air fromordinary atmospheric pres.-` sure, it may be compressed from only one vor two pounds pressure up to receiver pressure. This greatly increases the ratio of compres.. sion, and las the heat ent upon-the number of times the air is compressed, itwill readily. be seen that when the airreaches its iinal pressure in the air cylindenit willbe heated very much in excess' of the ltempera'tnre .ob-

A. FFT;

MONT, f u nur; MACHINERY SETES, A. CO'OB/ATION 01E SSAGHUSETTS. l l ce' Janssen' I speemrtionofettem Patent "llatented om'd, iltfl... Application led'lillay @,1912. Serialto,@95,87%l

` section enerat'ed in compres'l on an enlarged sc tained in compression under normal running conditions with the inlet opening wide open. This temperature is ldetrimental to the oil-used for lubrication, and -is a source of danger, inasmuch as the extreme-heat may ignite the oil,` and if the oil isdidused through the air in roper proportions an' explosion may -resullt This is especially dill true of multi-stage compressors where the a' three-stage compressor, or with the succeeding cylinders of a compressor of any.

and with slight lonT` cylinder of a multi-stage compres? desired number of stages, modification may be applied to the pressure 'sor or to the cylinder'of a single-stage compressor. 1

lln my copending application, Serial No.

695,875, ofvev'en date herewith, l have disclosed an elastic duid compressor-similar in Y its general characteristics to my present in. vention, but specifically did'erent therefrom, the present application, however,'being intended to dominate said copending a plication. Specically, the present application isfdistinguished from th cation' in that, in the latter, the auxiliary l unloading valve is seated by the pressurein of a spring, while in the intake plusthat the present case,`tl iev pressure in the outlet plus a spring is'applied to seat the'valve.

y invention will be y reference to the following description, when taken in connection with the accompanying illustration of one specic embodiment. thereof, While its scope will be more ar- 'ticularly pointed out in the appended claims: lln the drawings .l

Figure l is a central longitudinal' vertical partly-in r'ile'ifation of a compressor embodying myin'vention;

' Fig.2 is acrosssectional View of the coin- .pi'essor on line 2 2 of Fig. `l;

.Fig- 3 iS a lotudinal vertical section'- ae of one end of the cylin# @emmers er@ rhihwlinr der succeeding the l low-pressure cylinder oi? a multi-.Stage cylinders of e companion appli,

best understood' by Utl der in the present. embodiment is of the` fication of a portion of the valve mechanism.

Referring to the drawings, and to the embodiment of my invention which I have there disclosed for illustrative purposes, I have there shown a multi-stage compressor herein having two cylinders, a low-pressure cylinder 6 anda high-pressure cylinder 7, the former drawing its supply from an inlet pipe 8 into an inlet cham er 9 and delivering the compressed .air into an outlet chamber 10 connected 'by a pipe 11 to an yintermediate receiver 12, which as usual cools the air before i't paes to the high-pressure cylinder. This receiver, which is commonly called an inter-cooler, delivers the air into -an inlet chamber 13 of the high pressure cylinder 7, whence it passes to an outlet chamber 14, as will appear. hereinafter. This outlet chamber in ractice is connected to a main receiver whic I have not shown herein, as it unnecessary to thel illustration of my present invention. The main inlet 8 may be lcontrolled as is usual by means of i a main unloading valve 15 of the balanced type. This valve is usually controlled by a suitable piston, which moves to its open or closed position by means of a small regulator, which is piped to the main air receiver, these parts bein of usual and well.

known construction, an a further description of them being unnecessary to an understanding of my present invention.

The auxiliary unloadin valve which forms the subject matter o Vmy present invention `may be applied to any cylinder of a multi-stage compressor. In the form illustrated in Figs. 1 to 4 inclusive, it is shown as applied to any lcylinder beyond the first, or low-pressure cylinder,-that is. to say, it may be applied to the second or highpressure cylinder of a two-stage compressor, or to the second and third cylinders of a three-stage compressor; while Fig. 5 shows a' slight modification which Ihave made to adapt the auxiliary unloading valve tothe low-pressure cylin er of a multi-stage compressor, or tothe cylinder of a single-stage compressor.

to. Figs. 3 and 4, I have Referring now there shown one end of the high-pressure c linde;` 7 ,-.herein of the double-acting type,

t e other end being precisely similar 1n construction. "This cylinder is provided with a head 16, in which is located an inlet valve 17, whichsmay be of any usual or desired fthe air in the usual manner.

be of any usual construction, herein being provided with a spring 19 tending to seat the same and operating as usual to open and ermit the air compreedin the cylinder to ow'into the outlet chamber 14 and thence` to the usual main air receiver.

' Within the cylinder 7 is a usual piston 20, I

which when moved toward the right (Fig. 3) draws the air through the inlet chamber 13 andl its connections with the low-pressure vcylinder 6, and upon the closing of the inlet valve 17, as shown in Fig. 4, the piston moves toward the left, thereby compressing When the pressure in the cylinder is equal to, or slightly greater than, the pressure in the discharge chamber 14, the discharge valve '18 will lift from its seat to allow theair to be forced out of the cylinder.

To prevent the formation of a more or less complete vacuumwhen the unloading valve 15 onl the main inlet 8 closes, I have provided a valve 21 which is adapted to open or close the ort 22 leadin from the interior of the cylinder 7 to the inlet' chamber 13. This valve may be-of any suitable construction, but I have herein chosen to employ for this purpose a hollow shell, which is guided on a suitable guide, herein a plug 23. Suitable means are provided for establishing a communication between the interior of the valve 21 and the outlet cham- 'ber 14, so as to normally allow the pressure within said outlet chamber to be exerted f .on said valve in such a manner as `to 'tend -to seat the same. For-this purpose, the plug 23 is made hollow and' its interior is connected by a` pipe 24 to a small auxiliary cylinder 25. This auxiliary cylinder is. connected by a pipe 26 tothe outlet chamber 14. Located within the auxiliary cylinder 25 is a valve 27, herein of thepiston type, having a reduced portion 28 intermediate its ends. .When 'the compressorjis operating under normal conditions, the discharge'air pressure in the outlet chamber 14 is communicated through the pi e 26 around the reduced portion 28" o 'the valve 27 to the pipe 24, yand thence to the interior of the plug 23 and valve 21, 'thereby tending to seat the latter. This pressure maybe assisted if desired vby means of a suitable lspring 29,` tending to seat the valve 21. In the case of a double-acting of the cylinder. Inasmuch as the internal diameter ofthe valve 21 is somewhat greater 1.30

rare

than the diameter or the pmt 22, saiavalve in communication with the inlet space 13 of the cylinder, herein by a pipe 31. When the unloading valve on the main inlet to the low-pressure cylinder closes, air is no longer delivered to the cylinderin question,

- and as the latter continues to draw air from the space 13, the pressure in this space begins to fall. This space being in communication with one end of the auxilia cylinder 25, as just described, the drop 1n pressure soonreaches a point where the pressure acting against the end of the piston valve or plunger 27 isno longer sucient f to hold the latter in the position shown in when a suciently high pressure is reached, l

Fig. 3 against the pressure of the spring 32 bearing against the opposite end of the plunger. Accordingly, the plunger is forced over toward the-'right under the iniuence of the spring into the position shown in Fig. 4. When the valve is in this position,

the supply of air from the discharge'space 14 to the interior of the valve 21 is cut of, andV communication between the interior rof said valve and the atmosphere is established through the` pipe 24, the cylinder 25 and a vent opening 33. The pressure still remaining in theinlet space 13 and within the interior of the cylinder G will then be sucient to force the valve 21 from its seat, after which it is evident that no air will be discharged from this cylinder into the discharge space 14, but will return through the cylinder to the admission space 13 through the'port 22. x, i

When the unloading valve' on the inlet of the low pressure cylinder again opens, this cylinder will begin to deliver air to the inlet space 13. This pressure will be communicated through the pipe 31'to the righthand end of the piston or plunger 27, and

the latter will be forced back again into the position shown in Fig. 1, whereupon pressure will be .admitted to the interior of the valve 21, closing it, after which the nor- ,mal function of compression will be re` sumed. 4Incase it is desired -to attach the aum'liary unloading valve hereinbefore described to the low-pressure cylinder of a Y multi-stage compressor, or tothe cylinder of a single-stage compressor, a slight-modification may be'made, as shown in Fig. 5, in

' which the spring, herein a spring 34 similar tol the spring 32, is applied to the opposite end of the cylinder fromthat to whlch the spring'32 is applied, as shown in Fig. 3. lf'n other respects, the apparatus will vremain unchanged in its adaptation to the low-pressure Ycylinder of a multi-stage compressor orto the cylinder of a' single-stage compressor. Assuming that the unloading valve on the main inlet closes, a partial vacuum will be set u in the inlet space 13. lnasmuch as the le t-hand end of the plunger shown in Fig. 5 is exposed to atmospheric pressure through the vent-hole to the atmoshere, as soon as a'sucient diminution ofp the atmosphere below atmospheric pressure has beenreached, the plunger will be forced to- Ward the right, thereby cutting off the supply of pressure from the discharge space through the pipe 26, and the interior of the valve 21 will then be connected with the atmosphere through the pipe 24, the interior of the cylinder 25 and the vent-hole 33. rllhe air which may remain in the inlet 13 and which is drawn into the cylinder, Will be forced out through the port 22, before it reaches a pressure very much in excess of atmosphericl pressure, because of the fact that only atmospheric pressure is now existing in the interior of the valve 21. This will avoid the high ratio of compression on any.

air remaining in the interior of the cylinder or the passages leading thereto. While I have shown the application of these methods of unloading as applied to a singlestage compressor or the low-pressure cylinder of a multi-stage compressor, consider the auxiliary unloading valve especially desirable for attachment to the cylinder succeeding the low-pressure cylinder of the latter type of compressor. It will be understood from the foregoing that the auxiliary unloading valve acts automatically to prevent diminution of pressure 'in the connections between the high and low-pressure cylinders to a point below atmospheric pres- .sure when the main unloading valve closes,

or in other words,the auxiliary valve acts automatically to place the high-pressure cylinder in communication with the connections between the cylinders when the pressure within the said connections falls below normal.

WVhile l have herein shown and described two forms of my invention for illustrative purposes, and have disclosed and discussed but that extensive deviations from the illustrated forms or embodmentsof the inventhe principles thereof.

tion-may be made without departing from I claim: i

rae

1. 1n an elasticfluid compressor, the com- Y bination with means for drawing in and compressing the Huid, said means having an APly pressure within sai 50 intake valve; of a valve for controlling the supply of fluid to the com ressing means; connections between said va ves; and means distinct from said intake valve and actuated by the pressure in said compressing means effective to prevent diminution of pressure to a point below atmospheric pressure within said connections when the secondmen tioned valve closes.

2. In an elastic fluid compressor, the combination with fiuid compressing means having a mechanically actuated inlet valve and an outlet valve; of a valve controlling the supply of fluid to said inlet valve; connections between said controllin valve and said inlet valve; and means istinct from said inlet valve andv actuated by the pressure in said compressing means, to prevent diminution of pressure within said connections-to a'point below atmospheric pressure.

3. In an elastic fluid compressor, the combination with fluid compressing means; of an unloading valve for controlling the supply of Huid to the compressing means; and an auxiliary unloading valve opened bythe pressure within-said compressing means, for relieving the condition of pressure within the compressing means when the first-mentioned unloadin valve closes.

4. .In an elastic fluid compressor, the combination with fluid compressing means having an intake valve; of. an unloading valve for controlling the supply of iuid to the compressing means; and an auxiliary unloading valve distinct from said intake valve and opened by the pressure within'said compressing means, for preventing diminution of pressure within the connections between the first-mentioned unloading valve and the compressing means to a point below atmospheric pressure. i

5. In an elastic fluid compressor, the ccmbination with fluid compressing means having a mechanically actuated inlet valve and a pressure-duid opened outlet valve; of an unloading Vvalve for controlling the supply of fluid to the compressing means; and an auxiliary unloadin valve operated by the compressing means, for preventing diminution of pressure within the connections between the first-mentioned unloading valve and said inlet valve, to a .point below atmospheric pressure.- l i -6. In 'an elastic iuid compressor, the com'- bination with iiuid compressing means; o'f an unloading valve for controlling the sup# of Huid to the compressing means; and a valve seated by the pressure in the outlet and opened by the pressure within said oompressing means, for relieving the condition of pressure within the compressing means when the unloading valve closes.

7. In an elastic iuid compressor, the combination with fiuid compressin means; of

an unloading valve for controlling the supv y pressure tending to seat said unloading vlave and compressing means when said unloading valve closes.

8. In an elastic fluid compressor, the combinationl with fluid compressing means; of (an unloading valve for controlling the supply of fiuid from the inlet to the compressing means; an unloading valve normally closed by pressure in the outlet and subject to pressure within said compressing means; and means rendered effective by reduction of ressure in the connections between the filst-mentioned unloading valve and the com ressing means, to cut off the pressure ten ing to seat the second-meuf tioned unloading valve and permit the latter to open under the iniuence of pressure within the compressing means.

9. In' an elastic fluid compressor, the combination with a cylinder and piston, of admission and outlet valvesor said cylinder,

-an unloading valve :for controlling the sup- 'of pressure in said connections to cut off the I i pressure tending to seat the last-mentioned valve and permit the latter to open under the influence of the pressure within saidv cylinder.

10. Inl an elastic fluid compremor, the combination with a'cylinder and piston, of admission and outlet valves for said cylinder, an unloading valve for 'controlling the supply of-fluid to the'admission valve, said cylinder having an outlet port leading to the connections between said unloading and admission valves, a valve for saidport normally seated by pressure in the outlet and subject to the ressure withinsaid cylinder and means inc uding a valve normally held Y open by the pressure in said'connections and adapted to be released by a reduction of the pressure in said connections thereby to close under atmospheric pressure and yout off the the valve of said port.Y A 1v1. yIn an Aelastic fluid compressor, the combinationv witha cylinder and piston, of admission and outlet valves for said -cylinder, an unloading Avalve lfor controlling the suppl of fluid'to the admission valve, said cylin er having an. outlet port leading to the connectlons between said unloading-and admission v al;s 'esifaggvalv'el for said port normall seatedby pressure in the outlet and subject tothe pressurewithin sud-cylin-A,

llt)

means actuated by a reduction of the pres,

sure 1n said connections to allow the lastmentioned valve to close and. cut od the pressure tending to seat the valve of said ort. p 12. lln an elastic iluid compressor, the combination with a cylinder Vand piston, of admission and outlet valves for said cylinder, an unloading valve for controlling the supply of iiuid to the admission valve, said cylinder having an outlet port leading to the connections between said unloading and admission valves, a valve for said port norf mally -seated by pressure in the outlet and subject to the pressure within said cylinder, a valve adapted to control the pressure tending to seat the valve of said port, a spring tending to close the lam-mentioned valve,

and means actuated by la reduction of the pressure in said connections to allow Athe last-mentioned valve to close and cut od the pressure tending to seat the valve of said 25 port. Y

13. ln an elastic fluid compressor, the

combination with a cylinder and piston, ofl admission and outlet valves for said cylinder, an unloading valve for Acontrolling the supply of uid to the admission valve, said cylinder having an outlet port leading to the connections between said unloading and admission valves,-a valve for said port normally seated by pressure in thev outlet and subject to the pressure within said cylinder, a valve adapted to control the pressure tending to seat the valve of said port, and a valve-actuating piston connected to thelastmentioned valve acting under` normal conditions to hold said valve open but adapted Y to be actuated by a reduction cf the ressure vat ' v an unloading valve for controlling htl in said connections to allow the va ve .controlled thereby to close and cut 0H the pressure tending to seat the valve vof said port.

14. llnan elastic fluid compressor the combination with a cylinder and piston, of admission and outletvalves for said cylinder,

the supp`ly of vfluid to the admission valve, said cylinder having an outlet port leading to the connections between said unloading and admission valves, a'` valve for said port normally seated by pressure in the outlet and subject to the pressure within said cylinder, a piston valve adapted to control the pressure tendin to seat the valve of said port, and a cylin er for said piston valve having one end in communicatlon with said conl nections and the other end in communication 'with the atmosphere.

15. In an elastic Huid compressor, the

A combination with a cylinder and piston, of

admission and outlet der, an unloading supply of uid tothe admlssion valve, said valves for said cylinv pressing means,

valve for controlling the cylinder having an outlet port le my to the connections between said unloading d admission valves, a valve for said port normally seated by pressure in the outlet and subject to the pressure within said cylinder, a piston valve adapted tocontrol the pressure tendin to seat the valve of said port,

a cylinder or vsaid piston valve having one A end in communication with said connections and the other end in communication with the atmosphere, and a spring tending to .move said piston` valve into position to cut o the pressure tending to seat the valve of said port. V

16. ln van elastic Huid compressor, the combination with fluid compressing means; of a valve for controlling the supply of iluid to the compressing means; connections between said valve andV said compressing means; and means including a valve sub-A ject to Yand opened by pressure within said compressing means, to prevent diminution of pressure to a oint below normal inlet pressure within said connections when said valve closes.

17. In an elastic Huid compressor, the combination with fluid compressing means; of means forming an inlet ace; inlet controlling means; and automatlc means includsupply-space pressure iiuid previlously drawn from said supply space.

19. ln an elastic fluid compi-essor, the` combination with compressing means for drawing in and compressing the fluid. said compressing means having a periodically opening and closing intake valve and adischarge valve, of duid conducting meam for conducting the supply of Huidv to said .comand automatic means separate from said intake and discharge valves and subject to 'and opened by pressure within said compressing -means for releasing pressure duid therefrom into said Huid conducting means j 20. ln a multi-stage elastic sor, the combination with a plurality of compressor units acting successively to coinpress the elastic-plui d,f` of l a periodicaH opening and closing intake valve and a" discharge valve for the high pressure unit, and means independent of said intake and dis- Huid compresico roe

charge valves and subject to and opened by pressure within said compressing means for returning into the connection between said units elastic iuid that is drawn through said intake valve. A

21. In a multi-stage elastic fluid compres sor, the combination with a plurality of compressor units, one delivering to another and each having an intake valve arranged to open and close periodically, of a main unloading valve for the first stage compressor unit, and a hi h pressure unloading valve independent o the high pressure unit intake valve and subject to and rendered effective by the pressure within the high pressure unit.

22. In an elastic iiuid compressor, a cylinder, a piston, inlet and discharge valves for said cylinder, an unloadin valve, a connection between the latter an said inlet valve, a valve actuated by pressure in said cylinder controlling the communication between the latter and said connection, and controlling means for said valve responsive to variations in pressure in said connection.

23. I nan elastic uid compressor, a cylinder, a piston, inlet and discharge valves for said cylinder, an unloadin valve, a connection between the latter an said inlet valve, a pressure actuated valve in said cylinder controlling the communication between the latter and said connection, and controlling means for said valve responsive to variations 1n pressure 1n said connection for supplymg pressure iuid theretofrom said cylinder.

24. In an elastic liuid compressor, a cylin? der, a piston, inlet and .discharge valves for y said cylinder, an unloading valve, a connection between the latter and said inlet valve, a valve responsive to pressure in said cylinder controlling ,the communication between the latter and said connection, and controlling means for said valve responsive to a drop in pressure lin said connection below atmospheric pressure. i' y 25. In an elastic iuid compressor, a cylinder, a piston, inlet and discharge valves for said cylinder, an unloadin valve, a connection between the latter an said inlet valve, a pressure actuated valve` in said cylinder controlling the communication between the p latter and said connection, and controlling means for said valve responsive to a drop in pressure in said connection `below atmospheric pressure for supplying pressure Huid thereto from said cylinder. 26. In la multi-stage elastic fluid compressor, the combination with aplurality of compressor units acting successively to compress-the elastic fluid, and a main unloading valve, of a valve for the inlet of a high pressurecompressor unit, and means independentof said valve automatically to prevent diminution of pressure to a point below atmospheric `pressure in the connections piston, and one delivering to another,

sor, the combination with a plurality of compressor units one delivering to another, of a main unloading valve for the inlet of the first-Stage compressor unit, and an auX- iliary unloading valve. for the succeeding compressor unit discharging into the connections between said units when the pressure in said last mentioned unit exceeds a predetermined amount.

28. In a multi-stage elastic fluid compressor, ,the combination of a plurality of compressor units, one delivering to another, of a main unloading valve for the inlet of the first-stage compressor unit,- an inlet valve for the succeeding compressor unit, and means subject to pressure within said succeeding compressor unit automatically to prevent diminution of pressure to a point below atmospherlc pressure 1n the connec vtions between said compressor units when the main unloading valve closes.

29. In a multi-stage elastic iuid compressor, the combination of a plurality of compressor units each having a cylinder am; a o a valve for the inlet of one-.of said compressor units, an inletvalve for the succeeding compressor unit, and means subject to pressure within said compressor unit automatically to place the cylinder of said succeeding compressor unit in communication with the connections between the compressor vunits when the pressure in said connections falls below normal.

30. In a multi-stage elastic Huid compressor, the combination of a plurality of compressor units, each having a cylinder andl a piston, and one delivering to another, of. an unloading valve for the inlet of one of said' compressor units,y an inlet valve for the succeeding compressor unit, the cylinder of said succeeding` compressor unit having a port communicating with the connections between the lcompressor units, a valve ier said port, and means normally holding' the lastmentioned valve seated and adapted to permit said valve to open when the pressure in'said cylinder rises above a predetermined amount.

3-1. In a multi-stage elastic fluid compressor, the combination of a plurality of compressors units each having a cylinder and a piston, and one delivering' to another, of an unloading valve for the inlet of one of said compressor units, an inlet valve for the sucvalve, and a cylinder for said valve-actuating piston communicating on one side of the latter With the atmosphere and on the other side with said connections.

32. In a multi-stage elastic fluid compressor, the combination of a plurality of compressonunits each having a cylinder and a piston, and one delivering to another, of an unloading valve for the inlet of one of said compressor units, an inlet valve `for the succombination with compressing means for.

drawing in and compressing the fluid, said ycompressing means having an intake valve,

of' controlling means for controlling the supply of fluid to said compressing means, and

automatic means separate from said intake.

valve for releasing pressure fluid from said compressing means into the connections between said controlling means and said compressing means when the pressure in said compressing means exceeds a predetermined amount.

34. In an, elastic fluid compressor, the combination with compressing means for drawing in and compressing the fluid, said compressing means having a periodically opening and closing positively operated intake valve and a discharge valve, of fluid conducting means for conducting the 'supply of fluid to said compressing means, and automatic means separate from said intake and discharge valves and actuated by the pressure in said compressing means for releasing .pressure fluid from said compressing means into said fluid conducting means.

35. In a multi-stage elastic fluidcompressor, the combination with a' plurality of compressor units acting successively to compress the elastic fluid, of a periodically opening and closing positively operated intake valve and a discharge valve for the high pressure unit, and means independent of said intake and discharge valves and actuated by the pressure in said high pressure unit to by-pass back into Mthe connections between said units elastic fluid that is drawn through said intake valve.

36. In a multi-stage elastic fluid Vcompressor, the combination with a plurality of compressor units one delivering to another and each having a positively operated intake valve arranged to open and close periodically, of a main unloading valve for the first-stage compressor unit, and a high pressure unloading valve independent of the high pressure unit intake valve and subject to pressure Within the high pressure unit and opened thereby after closure of said main unloading valve.

37. In an elastic fluid compressor, in combination, a compression cylinder, a ineclianically actuated inlet valve and a spring held outlet valve therefor, an unloading valve for controlling the supply of fluid to said cylinder, an auxiliary unloading valve communicating with said cylinder and subject to the pressure therein, and means to apply fluid pressure to seat said valve, said means acting to reduce lsaid pressure to release said valve when the pre'ssure in the cylinder has changed undesirably because of the actionof the first mentioned unloading valve.

38. In an elastic fluid compressor, a cylinder and'piston, separate inlet and discharge valves for said cylinder, an unloading valve, a connection between the same and said inlet valve, a valve'in said cylinder controlling the communication between the latter and said connection, a second cylinder receiving fluid discharged from said discharge valve, a second piston working Ain said second cylinder having one end exposed to atmospheric pressure, means for connecting the opposite end of said second cylinder to said connection, andmeans controlled by said second piston communicating with the valve controlling the communication between said first cylinder and said connection.

39. In an elastic fluid compressor, a cylinder and piston, inlet and discharge valves for said cylinder, an unloading valve a connection between the same and said inlet valve, a valve in said cylinder controlling the communication between the latter and said connection, -a second cylinder receiving fluid from said discharge valve, a second ypiston Working in said cylinder having one FRED D. HOLDSWURTH.

IVitnesses:

THoMAsB.. BOOTH,

Evenm'r S. EMERY. 

